1. Field of the Invention
The present invention relates generally to recording charts of the type wherein scores are inscribed thereon, and more particularly, but not by way of limitation, to recording charts of the type used in oil and gas well bottom hole pressure testing apparatus.
2. Description of the Prior Art
Apparatus for testing various conditions in oil and gas well bores, i.e., drill stem testing apparatus, commonly include charts formed of metal or other material for recording pressure and other conditions in the well bore. Scores representing a recording of the particular condition tested are inscribed on the chart by a marking stylus. For example, bottom hole pressure recording devices are commonly utilized to record pressures in a formation penetrated by a well bore during testing of the formation. The pressure recordings are made on a metal chart by a marking stylus attached to the end of a bourdon tube positioned in the device. Pressure is transmitted through a rubber diaphragm to fluid contained within the bourdon tube causing the stylus attached thereto to be moved on the chart. The chart is driven past the stylus by a clock thereby recording pressure versus time on the chart.
Heretofore, the charts utilized in bottom hole pressure recording devices and the like have been formed of brass coated with a dark coating so that scores inscribed on the chart by the marking stylus of the recording apparatus penetrate through the black coating and form light-colored markings in a black background on the chart. While such charts can be readily utilized to determine the recorded information, copies of such charts using conventional photocopying equipment are generally unsatisfactory due to the dark-colored background and light-colored markings. Consequently, heretofore, it has been necessary to photograph the original metal chart, produce a negative having the light and dark colors reversed and make copies from the negative.
While attempts have been made heretofore to produce charts for use with drill stem testing apparatus which when scored by a marking stylus produce dark markings on a white background, such charts have largely been unsuccessful due to the high temperatures to which the chart is exposed while bottom hole tests are being conducted. By the present invention, a high temperature resistant recording chart and method of manufacturing such chart are provided wherein scores inscribed on the chart produce dark markings in a white background so that conventional photocopies of the chart and recordings thereon can be readily made.